At the early stage of building up a nation-wide Time Division-Synchronous Code Division Multiple Access network (i.e., TD network), the area covered by each operator in the network is limited. This situation can last for a certain period of time before each operator can suitably achieve nation-wide coverage. Roaming agreement between operators has been used in similar situations, so that a subscriber can make/receive calls when he roams into area (i.e., visited network) that is not covered by the network provider of the subscriber. In this manner, sharing network resources to allow TD subscribers to roam nation-wide is a cost saving alternative, which is beneficial to all participating operators.
One specific implementation of a TD network is a Public Land Mobile Network (PLMN). It is known that some adverse issues exist when implementing inter-PLMN roaming in a PLMN. Therefore, to suitably implement an inter-PLMN roaming feature, there exist technical issues that must be resolved. One issue that must be resolved is addressing differences in content of Intelligent Network (IN) service because such content is not the same for all PLMNs. Even for the same IN service, there are always minor differences in using a message's parameters. Due to the un-unified content and the varied usage of parameters, there is no assurance that a roamer can get the same IN service from a visited PLMN as he could get from the roamer's home PLMN. Another such issue that must be resolved is allowing a roamer's home PLMN operator to obtain certain information associated with a call originated in a visited PLMN. For example, for billing purposes, a roamer's home PLMN operator will often have a need to obtain certain information for a call originated by the roamer in a visited PLMN. Another such issue that must be resolved is how to route calls originated by roamers from a visited PLMN to a Gateway Mobile Switching Center (GMSC) of a Roamer's home PLMN to trigger Originating Camel Subscription Information (O-CSI) and to store the billing information. Still another such issue that must be resolved is how to gain full control of the call routing from within a network without depending on other networks. Still another such issue that must be resolved is how to minimize the impact of roamers to visited network capabilities such as, for example, call capacity, signaling traffic amount, etc. Yet another such issue that must be resolved is how to minimize the cost of necessary modifications and maintenance to all network nodes caused by the deployment of a solution that addresses all or a portion of these issues.
At least one attempt has been made at devising a solution configured for addressing the abovementioned issues associated with PLMN roaming. This solution was proposed by China Telecom and is based on enhancing a switch's function to meet the special roaming requirement in a PLMN. However, this solution has a number of shortcomings. One such shortcoming is that it requires the GMSC to temporarily download a calling party's profile from a Home Location Register (HLR), which breaks GMSCs characteristics of not having Visiting Location Register (VLR) logic. In addition, the subscriber's profile is stored in both VLR and GMSC, which also violates the associated standard network protocol. Another such shortcoming is the need to use both calling party and called party numbers (i.e., a tandem switch) for routing. Conflicting logic can cause the tandem switch to misroute a call, even to a normal call. As there is no thorough solution to the misrouting issue this proposed solution, this could be a potential fatal defect to the solution. Another such shortcoming stems from adverse cost and installation difficulty when the solution is widely deployed. For example, when the roamer originates a call in a visited PLMN, the visited PLMN is responsible for routing the call to the home PLMN's GMSC of the calling party. Prior to the call reaching the calling party's home GMSC, it relies on the visited PLMN to make the routing decision. Therefore, the routing logic made specifically for this proposed solution must be implemented and deployed in all network elements of all possible PLMNs, which adversely impacts cost and deployment. Still another such shortcoming is that a forwarding call invoked by a roamer cannot be routed back to the roamer's home PLMN. Yet another such shortcoming is that, to unify routing logic in the proposed solution, the originating network should route the call within the (originating) network as far as possible before routing the call into the terminating network. For example, a call is made from China Telecom in Beijing to a subscriber of China Unicom in Shanghai. The call should be routed within the China Telecom network to China Telecom in Shanghai and then routed in Shanghai to China Unicom. Such an implementation of Inter-PLMN roaming requires a separated network for both forward and backward directions. Otherwise, confusion will result when routing calls in a tandem switch. This type of network planning is an expensive requirement, especially when applying changes to all existing second generation (2G) tandem switches for supporting routing by calling number.
Therefore, a solution that overcomes shortcomings associated with known solutions and that allows for effective and efficient implementation of inter-PLMN roaming in a Public Land Mobile Network (PLMN) would be advantageous, desirable and useful.